This application relates generally to gas separation processes and apparatus, and more particularly, to CO2 sequestration.
The application of syngas conversion and purification, e.g., after the syngas is generated from coal gasification processes, can be used for integrated gasification combined cycle (IGCC) power plants for electricity production from coal, and IGCC-based polygeneration plants that produce multiple products such as hydrogen and electricity from coal, and is useful for plants that include carbon dioxide separation. It is also applicable to purification of other hydrocarbon-derived syngas which can be used for electricity production or polygeneration, including syngas derived from natural gas, heavy oil, biomass and other sulfur-containing heavy carbon fuels.
The commercialization of known ‘coal-to-hydrogen (H2) and electricity’ technologies (coal gasification-based polygeneration plants or IGCC power plants) has been hampered by the high capital costs associated with removing the impurities. The stringent purity requirements for hydrogen fuel and the fuel specifications for the gas turbine are generally satisfied using a series of clean-up unit operations, which facilitate carbon monoxide (CO) conversion, sulfur removal, carbon dioxide (CO2) removal, and final gas polishing. Some known syngas clean-up technologies focus on removing each impurity in a separate unit operation.
Raw fuel gas exiting the gasifier is cooled and cleaned of particulate before being routed to a water-gas-shift (WGS) reaction unit, which converts CO and H2O present in the syngas to CO2 and H2, thereby concentrating it in the high-pressure raw syngas stream. Also, in order to attain the desired CO conversion, highly excessive amounts of steam are generally introduced to the syngas stream in order to drive the WGS reaction to near completion. As a result, the WGS reaction demands large amount of energy to generate the excessive amount of steam that the reaction requires. The resulting syngas contains primarily H2, which is the desired product, and CO2 and other impurities (such as sulfur) that are to be removed prior to utilization of the H2.
Sequestration of CO2 from power plants and other commercial plants that generate large amounts of CO2 is desirable. Among existing types of CO2 capture technologies, the pre-combustion CO2 capture technologies, which remove CO2 from concentrated syngas stream at high pressure prior to combustion of the fuel, is usually more efficient and cost-effective for coal-gasification based power plant or H2 production plants than post-combustion CO2 capture technologies, which capture CO2 from low pressure exhaust stream that is diluted with nitrogen and oxygen after the combustion of the fuel. The cost of pre-combustion CO2 capture using commercially available technologies such as absorbent based technologies can be as high as $40/ton, which, although is much lower than the cost of post-combustion capture, is still much too high for carbon emissions reduction applications. Furthermore, carbon dioxide capture is generally estimated to represent three-fourths of the total cost of a carbon capture, storage, transport, and sequestration system.
Hence, there continues to be a need for highly efficient and simplified CO conversion and CO2 removal systems that reduce or eliminate other system components, increase system efficiency, and/or otherwise simplify the purification of a H2 stream.